The Principal Value Integral symbol

This symbol (an integral sign, ‘crossed’) does not appear in any of the fonts ordinarily available to (La)TeX users, but it can be created by use of the following macros:

\def\Xint#1{\mathchoice
   {\XXint\displaystyle\textstyle{#1}}%
   {\XXint\textstyle\scriptstyle{#1}}%
   {\XXint\scriptstyle\scriptscriptstyle{#1}}%
   {\XXint\scriptscriptstyle\scriptscriptstyle{#1}}%
   \!\int}
\def\XXint#1#2#3{{\setbox0=\hbox{$#1{#2#3}{\int}$}
     \vcenter{\hbox{$#2#3$}}\kern-.5\wd0}}
\def\ddashint{\Xint=}
\def\dashint{\Xint-}

\dashint gives a single-dashed integral sign, \ddashint a double-dashed one.

This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=prinvalint